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Re: branch delay slots

From: Boris Boesler <baembel at gmx dot de>
To: Ian Lance Taylor <iant at google dot com>
Cc: GCC <gcc at gcc dot gnu dot org>
Date: Wed, 12 Dec 2007 18:50:36 +0100
Subject: Re: branch delay slots
References: <0375011D-0C51-4101-801E-5AC4217DB0DC@gmx.de> <m3k5nkaqhq.fsf@localhost.localdomain>

Am 12.12.2007 um 16:21 schrieb Ian Lance Taylor:

Boris Boesler <baembel@gmx.de> writes:

  I "implemented" branch delay slots (define_delay) for my
architecture and I use the command line option -fdelayed-branch. But
branch delay slot filling is done just for a few candidates. Even for
the same rule within the same compilation unit (C file) it is done in
a few cases but not in all. How can this happen?


There are many possible reasons.  The first step is to look at the
dump file generated by -fdump-rtl-dbr.

Could have thought of this myself ..

Ok, I think I found it: GCC leaves control-flow operations as they are, if it can not place other operations in branch delay slots (represented as SEQUENCEs in GCC); or in other words: GCC does not represent empty delay slots.

Is this correct?

Boris

Follow-Ups:
- Re: branch delay slots
  - From: Richard Sandiford

References:
- branch delay slots
  - From: Boris Boesler
- Re: branch delay slots
  - From: Ian Lance Taylor

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